Generally, when diene-based rubbers are cross-linked with sulfur, it is known in the art that the cross-linked bonds are mainly comprised of polysulfide bonds which easily disassociate under heating and, therefore, are inferior in heat aging resistance. On the other hand, butyl rubbers have superior heat aging resistance, compared with diene-based rubbers, but have the problems of smaller reactive portions capable of being utilized for the vulcanization reaction and, therefore, a slow vulcanization reaction compared with diene-based rubbers and difficulty in co-vulcanization with the other diene-based rubbers. In view of these problems, as a vulcanization agent or co-vulcanization agent, a compound of a thiol/maleimide adduct having active hydrogen-containing groups and which, upon heating, releases a maleimide compound and generates thiol groups has already been proposed (see Japanese Patent Publication (A) No. 2004-277705). The compound set forth in this patent publication, when used as a vulcanization agent or covulcanization agent of butyl rubber, gives an unvulcanized rubber exhibiting a high storage stability and a rubber obtained by vulcanization exhibiting a high thermal stability. However, it is still necessary to prevent or delay the scorching of the unvulcanized rubber composition and to improve the tensile characteristics and the heat aging resistance of the vulcanized rubber. Therefore, the present inventors found a compound which is capable of preventing or delaying the scorching of an unvulcanized rubber composition and of improving the tensile characteristics and heat aging resistance of the vulcanized rubber, that is, an N-substituted succinimide thio group-containing carboxylic acid metal salt, which was previously filed as a Japanese Patent Application No. 2005-296241.